How do you know that something is good or bad, right or wrong?

For me, I always use the virtue approach as well as the fairness or justice approach to determine whether this things or this behavior is right or wrong.  To be more specific, I always think about “does the action help or harm the individual’s character, or soul or does this act transmit true energy?” In the real life situation, when I was in primary school, one of my classmates always stole my stationery. As we can see, this is a really tiny thing, but it can become so big.  Like this kind of behavior has seriously violated morality and justice, ( He acquired something that did not belong to him by improper behavior) so that I know this is bad and wrong.